Vehicles equipped with pneumatic tires have come under increased scrutiny as requiring more detailed information regarding tire pressure. Such tire pressure information is required for safe operation of the vehicle and for greater fuel efficiency (in the case of motor vehicles) since underinflated vehicle tires cause increased fuel consumption compared to properly inflated tires. To monitor tire pressure, various systems have been proposed. In general, tire pressure monitoring systems include a pressure monitor and an element which can transmit the tire pressure information, typically in the form of a radio frequency (r.f.) signal, to a receiver inside the vehicle. In this manner the tire pressure information can be displayed and/or alarms can be set to alert the operator of the vehicle when one or more tires has reached a critical level of underinflation or overinflation.
Several configurations have been proposed which use an antenna positioned in the tire along with a tire pressure sensor also positioned within the tire. Such systems are depicted in U.S. Patent Application Publication 2009/0007648 and U.S. Pat. No. 5,040,561. However, antennas positioned within the tire may be subject to shielding by the tire hub, resulting in diminished signal strength reaching a receiver positioned elsewhere on a vehicle.
Other configurations use one or more sections of the tire valve itself, such as the valve stem or the valve pin as an antenna or an antenna portion to transmit a signal from an internal tire pressure sensor to a receiver for display/alarm concerning the tire pressure to the operator of the vehicle. Such systems are disclosed in U.S. Pat. Nos. 6,101,870, 7,059,178, 7,328,609, 7,549,329 and U.S. Patent Publication 2008/0121031.
However, there remains a need in the art for an improved tire pressure monitoring system with improved antenna gain and improved impedance matching.